Synopsis The owner of the PA-12 was conducting a demonstration flight with a prospective purchaser who was occupying the rear seat of the aircraft. Immediately after taking off from the High Prairie Airport, the aircraft climbed steeply to approximately 150 feet above the runway, pitched nose down, and plunged vertically to the ground. A post-crash fire ensued and both occupants sustained fatal injuries. The Board determined that the aircraft stalled on departure for reasons unknown. The low altitude at which the stall occurred precluded a successful recovery. 1.0 Factual Information 1.1 History of the Flight The owner/pilot was selling his Piper PA-12 and had arranged for a prospective purchaser to examine the aircraft at the High Prairie Airport, Alberta. The purchaser and an aircraft maintenance engineer (AME)1 had been flown to High Prairie in a private aircraft on the day of the accident. The owner/pilot had flown the PA- 12 to High Prairie from his nearby farm and landed after the private aircraft. The three men walked around the aircraft and spoke briefly while on the airport ramp. The owner/pilot then agreed, at the purchaser's request, to take the purchaser on a short demonstration flight. The aircraft was observed to perform a normal take-off roll on runway 07. Immediately after lift-off the aircraft climbed steeply to approximately 150 feet above ground (agl), pitched nose down, entered a one-quarter turn spin, and plunged vertically to the ground. An intense post-crash fire ensued and both occupants sustained fatal injuries. This accident occurred at 1022 mountain daylight time (MDT)2 during the hours of daylight at latitude 5523'N, and longitude 11628'W. 1 See Glossary for all abbreviations and acronyms. 2 All times are MDT (Coordinated Universal Time minus six hours) unless otherwise noted. 1.2 Injuries to Persons 1.3 Damage to Aircraft The aircraft was destroyed by the severe impact forces and the intense post-crash fire. 1.4 Other Damage No other significant property damage occurred. 1.5 Personnel Information 1.5.1 General 1.5.2 The Owner/Pilot The owner/pilot was characterized as a successful, self-employed farmer, and businessman. He had obtained his private pilot aeroplane licence in 1978. The licence was valid for single and multi-engine land aeroplanes, with a night rating and a current licence validation certificate. He had owned the PA-12 since 1987 and had owned several other aircraft previously. He had flown approximately 10 hours in the 12 months prior to the accident. There was no evidence that he had received recurrent dual training in recent years. His hobby interests had recently changed and he had decided to sell the PA-12 due to low utilization. He represented the aircraft as a good performer and had been discussing the performance advantages of the Borer propeller installation with the purchaser immediately prior to boarding the aircraft for the demonstration flight. 1.5.3 The Purchaser The purchaser held a private pilot licence, with a current licence validation certificate, valid for single and multi-engine land and sea aeroplanes, with a night rating. He had placed a pre- purchase deposit on the aircraft before travelling to High Prairie. 1.6 Aircraft Information 1.6.1 General Manufacturer - Piper Aircraft Corporation Type - PA-12 Year of Manufacture - 1947 Serial Number - 12-2740 Certificate of Airworthiness (Flight Permit) - Valid Total Airframe Time - 2,134 hours Engine Type Avco Lycoming O-320-A2B (number of) - (1) Propeller/Rotor TypeMcCauley 1A175-GM8241 (number of) (1) Maximum Allowable Take-off Weight - 1,750 pounds Recommended Fuel Type(s) - 80/87 minimum grade aviation Fuel Type Used - Unleaded automotive 1.6.2 The Aircraft The aircraft was fitted with dual controls. The aircraft was not fitted with a stall warning device, nor was one required by existing regulations. A review of the log-books indicated that the aircraft had last been inspected and certified on 20 April 1994. The pilot had since flown approximately three and one-half hours. The aircraft was at or near the maximum gross weight of 1,750 pounds and the centre of gravity (C of G) was within the prescribed limits. Several modifications had been incorporated on the aircraft. A 150-horsepower Lycoming O-320-A2B engine had been installed in accordance with Supplemental Type Certificate (STC) SA83AL, and a McCauley 1A175-GM8241 (Borer) propeller had been installed in accordance with STC SA279AL. Piper PA-12s were originally fitted with Lycoming O-235 series engines producing 100 to 115 horsepower. The aircraft had been fitted with larger tires in accordance with Transport Canada Approval Number W89-114. The aircraft had also been fitted with Piper PA-18 elevators. STCs exist for the tailplane modification; however, there was no STC approval identified in the aircraft records. The aircraft was not equipped with flaps. The aircraft was fitted with the original single-pulley cable-operated pitch trim system. Slippage of the trim cable is a common service problem in this model of aircraft; however, the pilot had not reported this to have occurred in the past and no log entries pertaining to trim slippage were found. During the investigation, it was determined that the owner/pilot was using unleaded automotive fuel in the aircraft. There was no evidence that the required log entries had been made or that an STC or Supplemental Type Approval (STA) permitting the use of automobile fuel had ever been incorporated on the aircraft, as required by Transport Canada document TP 10737, Use of Automotive Gasoline (Mogas) in Aviation. 1.7 Meteorological Information Good visual meteorological conditions existed at the time of the occurrence. A witness estimated the winds to be easterly at 5 to 10 knots. A supplementary aviation weather observation, taken approximately 10 minutes after the accident, recorded the sky condition as 7,000 feet scattered, visibility greater than 15 miles, and winds 140 degrees true at 22 knots. The temperature was 25 degrees Celsius. 1.8 Communications A UNICOM air-to-ground communications facility, operated by the Airport Manager, existed at the airport. The designated Aerodrome Traffic Frequency (ATF) was 122.8 megahertz (MHz). There was no reported communication with the aircraft on the ATF frequency. 3 Units are consistent with official manuals, documents, reports, and instructions used by or issued to the crew. 1.9 Aerodrome Information The High Prairie Airport is a registered airport. Runway 07/25 is 3,272 feet long and 75 feet wide. The runway surface is asphalt. The aerodrome elevation is 1,974 feet above sea level (asl)3. 1.10 Wreckage and Impact Information The aircraft came to rest on the flat graded area about 1,640 feet from the threshold of runway 07 and approximately 47 feet to the north of the runway edge. The wreckage was spread within a very limited area. Damage and ground scars indicated that the aircraft had struck the ground in a near-vertical, nose-down attitude. The forward legs of the pilot's seat were found detached from the supporting structure. The seat assembly was forwarded to the TSB Engineering Branch Laboratory to determine if this had contributed to a loss of control. An examination determined that the pilot's seat was structurally intact prior to impact, and there was no evidence of the seat being in a weakened condition prior to the accident. The crash loads far exceeded the design ultimate loads of the seat. The PA-12 utilizes a variable incidence horizontal stabilizer for longitudinal trim. The leading edge position is adjusted through the stabilizer yoke which has a range of travel of approximately 17 threads on the stabilizer adjustment screw. Post-crash examination of the horizontal stabilizer determined that the stabilizer yoke was positioned approximately one thread from the bottom of the stabilizer adjustment screw. This positions the leading edge of the horizontal stabilizer near the bottom limit of travel. The effect is a nose-up trim condition. Due to the almost complete destruction of the aircraft by the crash and fire, it could not be conclusively determined whether any pre-impact failure or system malfunction contributed to this accident; however, none was identified. 1.11 Medical Information There was no evidence that physiological or psychological factors affected the pilot's performance. Post-mortem examination of both occupants did not identify any evidence of incapacitation. The owner/pilot was occupying the front seat of the aircraft. Severe thermal injury to the hands and feet of both occupants made it impossible to determine which individual was operating the aircraft controls at the time of the crash. 1.12 Fire Both wing-mounted fuel tanks ruptured at impact. The intense, fuel-fed, post-crash fire consumed all of the airframe fabric covering and the cabin interior. The High Prairie Municipal Fire Department responded to the accident after being notified by the airport manager. 1.13 Survival Aspects The accident was not survivable as impact forces exceeded the limits of human tolerance. The aircraft was fitted with seat-belts which utilized obsolete metal-to-fabric type buckles. The aircraft was not fitted with shoulder harnesses. The emergency locator transmitter (ELT) was destroyed by the post-crash fire. 1.14 Tests and Research After the accident, an experienced PA-12 pilot and owner conducted trial flights in a similar aircraft, in different configurations, to ascertain the control forces with a nose-up trim condition. The trials revealed that a pilot should be able to physically over-ride the nose-up trim condition, as in the occurrence aircraft, to maintain the desired attitude and climb airspeed. 1.15 Additional Information 1.15.1 Landing Trim Setting The pilot was observed to perform a normal three-point landing on arrival at the High Prairie Airport. Weight and balance calculations determined that with only the pilot on board, the C of G would have been near the forward limit. The three-point landing would have been most easily accomplished with the trim near the full nose-up setting. 1.15.2 Piper PA-12 Operating Limitations The Piper PA-12 Handbook of Operating Limitations and Information states that the aircraft's stall speed is 49 mph true indicated airspeed (TIAS). The best rate-of-climb speed is identified as 75 mph TIAS in the normal category. It was not determined what airspeed the pilot normally used for climb. A witness reported that the engine appeared to be at full power when the nose of the aircraft pitched down and that the power appeared to have been reduced and reapplied an instant before the aircraft struck the ground. 1.15.3 Stabilizer Yoke Orientation During the investigation, it was noted that the horizontal stabilizer yoke assembly was installed with the flat side up. In the PA-12 Parts List, the stabilizer yoke is illustrated as being installed with the flat side down. Consultation with the manufacturer determined that the stabilizer yoke is oriented upside-down in the Parts List illustration, and that the stabilizer yoke was correctly installed in the aircraft. 1.15.4 Minimum Liability Insurance Although not considered a factor in the accident, the aircraft was being operated without the minimum liability insurance required by Air Regulations , Series VI, No. 10.